The present invention relates to a molded article with partial metal plating and to a process for the production of such molded article such as a circuit board, connector, etc.
A process for the production of molded articles having partial plating has been disclosed in Japanese Patent Application laying-open No. 61-239694 which has been filed on the basis of U.S. patent application Ser. No. 704,440. This Japanese application specifies several production processes of which two processes will now be explained.
The first process for production includes a molding process of the molded articles, an adhesion promotion process and an adherent metal plating process.
In the molding process of the molded article, an alternate two shot injection molding is used. In the first shot, the first portion of the molded article equipped with a circuit pattern is molded using a first electrically insulating material, while in the second shot, the supporting structure is formed around the circuit pattern using a second electrically insulating material. Polyethersulfone with catalyst is used as the first electrically insulating material for forming the molded article, and the appropriate catalyst for filler material is palladium catalyst scattered on powdered aluminium silicate. The catalyst mixed in the electrically insulating material is catalytic for the material for electroless metal plating to be conducted in the adhesive metal plating. The desirable second electrically insulating material to be selected for the supporting structure is polyethersulfone (without a catalyst).
In the adhesion promotion process, the surfaces of the molded article are made micro porous and hydrophilic and the catalyst on the surface part of the circuit pattern and hole walls are exposed. Accordingly, all the flat, smooth and glittering surfaces of the molded article are matted. Further, in the metal plating process, the molded article is passed through the vapor of dichloromethane, and the matted hydrophilic surfaces of the support structure will be made flat, smooth and hydrophobic so that they can endure the metal plating from outside and once again will be returned to the metal plating solution. The reason why these kinds of processes are required is to avoid non-uniform dispersal of the palladium catalyst, and avoid having the surface layers of the circuit pattern from becoming rich with the resin portion such that the catalytic function of the surfaces are not brought into full play.
In the second production process the molded articles are formed by a two shot process, where not only the first electrically insulating material to be used in the first shot process for forming the circuit pattern, but also the second electrically insulating material to be used in the second shot molding process for molding the support structure are selected from a material having no catalyst. The molded articles are treated with etching solution for adhesion promotion, then catalyst for metal plating is added and further is activated for electroless metal plating, and then non-adhesive catalyst is washed away from the support structure, and finally the circuit pattern is subjected to copper plating using a solution for electroless copper plating.
Both processes mentioned above involve the following problems.
The first problem in the production process of the former case is that palladium catalyst is mixed into the first electrically insulating material for forming the circuit pattern. Palladium is an expensive precious metal. It needs to be mixed in a large quantity in order to cause it to conduct as a catalytic function for electroless metal plating, and accordingly, economical production is difficult. The second problem is that the former case makes the production process complicated and deteriorates the working efficiency, since a process for making the matted surfaces flat and smooth is needed in the metal plating process in addition to the need of the process to make a mat on all the smooth surfaces of the articles in order to expose the catalyst.
The problem in the production process of the latter case is that it requires work to wash away with spray the catalyst adhered to the portions other than the circuit pattern, that is to say, all the surfaces of the support structure, after activation of the molded articles but before electroless copper plating. It is time-consuming to ensure the removal of the catalyst. Especially, the work to wash away the catalyst adhering to the surface of the border portion of the circuit pattern and support structure takes a great deal of time, labor, and expense and is practically difficult. When the removal of the catalyst is incomplete in the molded articles, for instance, in the circuit boards, portions other than the circuit portions will be sure to get metal plated, and the insulation of these portions is not secured. Therefore, they will not function as circuit boards.